Keithley 2562 Meas are Low in High R free download

File name 2562 Meas are Low in High R.pdf

A G R E AT E R M E A S U R E O F C O N F I D E N C E Problem: Measure- ments are Low in High Resistance Measurements There can be several reasons for measure- Remedy cancel the offset by selecting the correct ments that read low when making high resis- Use the force voltage and measure current reading range and using the zero function tance measurements. technique to measure the high resistance. In of the meter. this technique, the unknown resistance is put B. Use the alternate polarity technique. Off- Probable Cause: in series with a picoammeter or electrometer set currents may be due to charge stored Low Insulation Resistance ammeter and a constant voltage is applied. in the material (dielectric absorption), The insulation resistance of the test fix- This voltage can come from the picoamme- static or triboelectric charge, or piezo- ture could be in parallel with the device un- ter's internal source function or an external electric effects, and can be equal to or der test. source. Since the ammeter has very low re- greater than the current stimulated by sistance, essentially all the voltage appears the applied voltage. To use the alternat- Remedy across the unknown resistance. The resulting ing polarity method, make the measure- Use a test fixture and connecting cables current is measured by the ammeter and the ment once and record the result. Then with higher insulation resistance. The use of resistance calculated using Ohm's law. reverse the polarity of the applied voltage a driven guard also effectively increases the and measure again. Taking the average shunt resistance. Probable Cause: Offset Current of the readings should give an accurate result. The polarity reversal process can Probable Cause: Remedies be repeated any number of times, and the Low Input Resistance in the Meter A. Adjust the zero baseline of the meter. Me- resistance calculated based on a weighted The input resistance of the voltmeter